Portable or disposable ink jet printheads having attached ink reservoirs require provision to contain the ink during handling as well as in use. Without some provision for containing the ink when the orifice plate is face down, only the surface area mechanics at the orifices operate to contain the ink and this is usually inadequate.
Various techniques for preventing ink leakage at the orifice plate have been proposed. Probably the simplest is to apply a pressure sensitive adhesive tape to the orifice plate to seal the orifice. However, the removal of such tape places the delicate orifice plate at risk to damage and may induce ink leakage at one or more of the orifices. Additionally, the adhesive material if in contact with the orifice plate adjacent to and over the orifices may contaminate the orifices or change the characteristics of the orifice plates sufficiently to degrade print quality.
Foam is also used in the reservoir to retain the ink. Hereagain, surface energy mechanics is a factor in retaining ink in the interstices or the cells in the foam. Pressure reductions when ink is ejected by the ink head are usually sufficient to maintain an uninterrupted ink supply at the orifice plate. Volumetric effeciency however in the use of foam is only about 60 to 65 percent in most applications.
U.S. Pat. No. 4,509,062 entitled "Ink Reservoir With Essentially Constant Negative Back Pressure", issued Apr. 2, 1985 and assigned to the assignee of this invention adresses this problem in an arrangement which maintains a substantially constant negative back pressure slightly greater than the maximum anticipated ink hydrostatic head. This negative back pressure is maintained by the utilization and maintenance of a nonlinear force in an elastic section of the ink reservoir of the printhead.